When we interfere in the bidding and our partner (the Advancer) bids a new suit then when we have a fit we need to know our options for how to support them. We look at those options here.
One of the most important parts of bridge is raising partner. We try to raise Opener whenever possible. We may choose not to support partner immediately if we feel we have something more pressing to communicate, in which case we can respond in our own Major, use a negative double, or bid some number of notrump, but in general we strive to “support with support.”
When we open a NT and partner uses an artificial conventional responses, like Stayman or Transfers, then the opponents might double as lead directing. We want to use this double against them. Here we discuss our options for bidding after this double.